It is known to use a refrigeration unit having a binary compression refrigeration circuit to create low or high temperature within a vapor compression refrigeration circuit.
Units having such a binary compression refrigeration circuit include, for example, the refrigeration unit described in Patent Document 1. In this refrigeration unit, a low temperature-side refrigeration circuit is formed of a compressor, a condensation section of a cascade heat exchanger, an expansion valve and an evaporator, which are connected in order using refrigerant pipes, and a high temperature-side refrigeration circuit is formed of a compressor, a condenser, an expansion valve and an evaporation section of the cascade heat exchanger, which are connected in order using refrigerant pipes.
Generally, in a refrigeration circuit, the compressor efficiency is deteriorated in proportion of increase of a compression ratio. In particular, a unitary compression refrigeration circuit compresses and delivers refrigerant from the evaporator located on a low temperature-side section of the circuit to the condenser located on a high temperature-side section at one time at a high compression ratio, so that the compressor efficiency is not good. By contrast, if the binary compression refrigeration circuit is used, the compression ratio of the compressor of the high temperature-side refrigeration circuit and that of the compressor of the low temperature-side refrigeration circuit can be kept low, and the compressor efficiencies are improved.
For example, the hot-water supply system described in Patent Document 2 uses a binary compression refrigeration circuit, so that it is possible to perform high-temperature hot water supply through low temperature-side and high temperature-side refrigeration circuits, and even properly perform mid-temperature hot water supply through the low-temperature refrigeration circuit.
For example, the heat-pump hot-water supply system described in Patent Document 3 uses a binary compression refrigeration circuit, so that it is possible to perform preheating through a low temperature-side refrigeration circuit and also perform high-temperature hot water supply through the low temperature-side refrigeration circuit and a high temperature-side refrigeration circuit.